The instant invention is related to molding operations, and more particularly to an apparatus and preform specifically designed for obtaining proper orientation of the preform prior to its transport into a blow mold.
During molding operations, a preform or the like is typically moved through the system so that various operations can be formed on it. Due to cost considerations and various mechanical limitations which inherently exist within most systems, it is necessary that the preform be presented to the particular operations in a usable orientation. That is, it is generally not cost effective to present a preform in a random orientation and orientate the machine relative to the preform. As a result, efforts have been made to orientate the preform prior to its presentation to the various operations comprising the system. For example, orientation of a preform for blow molding operations is frequently required when a thread on a blown bottle or the like must be accurately located in order to position a closure thereon.
In blow molding operations, either a single stage or a two-stage process can be used for facilitating the molding of a preform for forming a container or other article. The two-stage process has a particular advantage over the one stage process. That is, the injection molding and the blow molding operations can be individually and separately designed to optimize the efficiency of each. In one stage processes, efficiency must generally be compromised in either one of the blow molding or injection molding operations steps since they are directly coupled. However, one stage blow molding processes are generally capable of maintaining the angular orientation of a preform for presentation to the blow mold, because the operations in the one stage process do not release the preform. This allows for orientation to be maintained between the injection molding and blow molding operations.
The two-stage process, by definition, requires that the preforms are released, which results in a loss of orientation. Further, the reheating and conditioning processes involved in a two-stage process are normally carried out by rotating the preforms as they pass through a system of ovens. Therefore, orientation is also lost through rotational movement. Such loss in orientation is only avoidable by using complex and expensive self aligning mechanisms which are generally not cost justified. For two-stage blow molding operations and for other operations requiring the orientation of articles, the prior art does include apparatuses and systems for accomplishing the orientation of articles. Generally, however, these apparatuses are complex and inapplicable to existing machinery without major alterations thereto.
U.S. Pat. No. 4,483,436 to Krishnakumar et al. describes a preform holding apparatus consisting of a bore through a pallet in which a rotatable collet is located for retaining the neck of a preform. The preform is retained in the collet by a spring loaded arrangement of detent balls which engage a circumferential groove between the flange and the thread of the preform. To retain the preform, the detent balls must pass over the molded threads to engage the groove. The preform rotates with the collet which is frictionally driven as it moves through ovens or the like. While this apparatus teaches a means for engaging and retaining a preform by its neck for a two-stage injection blow molding process, it does not disclose how to properly orientate the preform for the various operations. This apparatus also has potential for damaging the neck finish of the preform since the detent balls must be forced over the threaded portion.
U.S. Pat. No. 4,664,248 discloses a device and method for orientating blown articles carried randomly by individual pucks on a belt conveyor. The pucks have integral means for engaging the blown articles and for holding the same in a desired orientation. Such means consists of a peripheral slide surface positioned parallel to the desired direction of travel and a rotation producing surface positioned between the base of the puck and the slide surface. Each puck is necessarily rotated for acquiring the desired orientation. For a two stage blow molding operation, additional components would have to be assembled and positioned in order to orientate the pucks and then transport the pucks to the multiple cavities of the blow mold. Orientation would have to be accomplished for each puck after movement through the ovens, thereby requiring individual orientation mechanisms and making such a device particularly complex and expensive.
U.S. Pat. No. 3,576,247 to Caulford et al. describes a method of orientating metal cans. The method and mechanism uses a thick seam on the bottom of the can in order to establish the orientation. Extending walls of the cans are secured by a channel within a guide. The channel is slightly narrower than the thickness of the wall of the container at the location of the seam. The channel guide is formed in a pallet which is carried by a conveyor which moves adjacent a mechanism which induces rotation to the cans. As the can is rotated, the portion of the extended can wall having the larger thickness is caused to abut the outer edge of the channel. As such, the can is prevented from further rotation and this orientation of the can is used as a reference. The Caulford device uses a portion inherent in the can structure for facilitating the proper orientation. As such, the device is limited for use with cans having these thicker seams.
U.S. Pat. No. 4,212,841 to Michel discloses a device for manufacturing hollow thermoplastic articles. In this apparatus, preforms are produced from thermoplastic materials by a molding operation. Each preform is formed with a false neck having at least one positioning lug thereon. The positioning lug on the false neck is used to orientate the preform in an angular position relative to the blow mold such that the blow mold may properly engage the preform. Orientation of the preform via the positioning lug is carried out by a series of grippers which first rotate the preform for engagement by a second series of grippers which stop the rotation of the preform and engage the positioning lug. The series of grippers used for stopping rotation are movable relative to the preforms and must establish position relative to each presented preform to engage a positioning lug. In accordance with these requirements, both the rotation inducing grippers and the rotation stopping grippers include somewhat complex mechanical designs and electrical circuits. The apparatus disclosed in the Michel patent requires that the system be specifically designed for use with the positioning grippers. That is, such a system would be hard to incorporate into already existing machinery. In addition, because of the use of the false neck in the Michel apparatus, additional steps requiring the removal of the false neck must be taken at some point which increases cycle time and expense in forming the final product.
U.S. Pat. No. 5,282,526 to Gibbemeyer discloses a method for orientating container preforms. The apparatus disclosed uses a plurality of pallets which support pairs of rotating mandrels for moving preforms, closed end down, to and through an orientation station. At the orientation station, the preforms are rotated with the mandrels, via individual rotary drive means, until an individual pawl engages a notch on each preform. Each pawl engagement is detected by a limit switch on each mandrel. Once all the pawls are engaged, a bumper is lowered by an actuator to engage a brake assembly which, when engaged, prevents further rotation of the mandrels. After the first pawl engages the first notch, a slip clutch is used which allows the drive motor to continue to rotate while associated drive elements stop. The actuator is then retracted to allow the pallets and mandrels to be released. This apparatus is complex and requires that the pallets be stopped at the orientation stations for the individual stations to orientate the preform. The necessity to stop the pallets for orientation presents problems in incorporating this design into continuous motion automated systems. Due to the individualized treatment necessary for orientating each preform on each pallet, the orientation station includes a complex arrangement of moving parts. Also, because orientation takes place at a stopped position, orientation is a lengthier process than it would be with continuous motion machines.
There exists a need in the blow molding art, for a simple and economical system for fully orientating freely rotatable preforms for and prior to their presentation to a blow mold, wherein the system can be used with different sized and shaped preforms and with current systems by relying significantly on the design of the preform.